“You don’t think about disability when you’re out running. We’re just part of the community, we’re just like everybody else.”

David and Sandra Kerr welcomed their son, Aaron, in 1997, but when he was born, it was clear he had “some medical complications”. Now 25, Aaron is non-verbal and has a series of complex needs including cerebral palsy, epilepsy, and a chromosome disorder which means he uses a wheelchair.

At the age of 13, he underwent a kidney transplant, the organ donated by his father, but it was at that point that Sandra started to struggle mentally.

“At the time, I just went into automatic, and just did what I had to do,” she tells BBC Sport. “A few months afterwards, when things settled down, even though Aaron was doing very well, the enormity of it just hit me.”

Sandra tried medication and counselling, but it was running that did the trick.

“It was like she was her old self, it did so much for her, not just physically, but for her mental health it was really having a benefit,” says David.

“I thought was there a way that we could get involved somehow as a family, we would stay fit, it would help our mental health, and it would give Aaron something as well.

“It’s indescribable almost. For the first time in I don’t know how long, we actually felt that we were part of something.”

That was in 2014. Eight years on, the Kerr family, from Annahilt, Northern Ireland, have completed 49 marathons to date, including Dublin and Manchester, with David and Sandra pushing Aaron in an adapted wheelchair.

Next up on the calendar is the “iconic” London Marathon, a race they have long wanted to do, but this year marks the first time in which they are permitted to enter.

Until 2022, wheelchair participants had to complete the 26.2 miles from Greenwich to Westminster under their own power, with no assistance.

For seven years, the Kerrs have lobbied against the rule but until recently, their campaigning had proved fruitless.

“We were delighted this year when London Marathon approached us and asked us to be part of the consultation process on the inclusive future of the event,” says David.

“We had meetings over the last 10 months or so to try and find a way forward so that assisted runners could take part.”

As a result, four assisted wheelchair participants, including Aaron, are taking part in Sunday’s marathon. A maximum of four support runners per participant can help, though only two can push the wheelchair at any one time.

It’s a huge win for the Kerrs, and one which will make lining up this weekend all the more special.

“He just makes us laugh every day,” says Sandra. “Aaron is just so positive, and with all the issues he has to deal with, it just amazes us just how happy he can be every day.”

David adds: “Aaron is non-verbal, but he has a voice, he’s got something to say.

“People see him out on the road and he is happy, and he wants to hug and high-five everybody. What people don’t see are the hard days that Aaron has, and that’s really difficult for him.

“To see him go out and achieve what he’s achieved, we couldn’t be more proud of him.

“We’re just really looking forward to seeing this guy have a great day out, because he’s earned it and he deserves it.”